The present invention relates to electrical stimulation for treating chronic pain and, more particularly, systems and methods for delivering stimulation that can also monitor cardiac function.
The present invention may be used with spinal cord stimulation therapies in which a neurostimulator is used to stimulate dorsal column nerves. Spinal cord stimulation (SCS) systems treat chronic pain by providing electrical stimulation pulses through the electrodes of an electrode array placed epidurally near a patient's spine. SCS is a well-accepted clinical method for reducing pain in certain populations of patients. SCS systems typically include an Implantable Pulse Generator (IPG) coupled to an array of electrodes at or near the distal end of an electrode lead. The IPG generates electrical pulses that are delivered to neural tissue, e.g., nerve fibers within the spinal cord, through the electrodes of the electrode array.
In one type of SCS system, the electrodes are implanted proximal to the dura mater of the spinal cord. Individual electrode contacts (the “electrodes”) may be arranged in a desired pattern and spacing in order to create an electrode array. Individual conductor wires can connect with each electrode in the array. The electrode leads exit the spinal cord and attach to the IPG, either directly or through one or more electrode lead extensions. The electrode lead extension, in turn, is typically tunneled around the torso of the patient to a subcutaneous pocket where the IPG is implanted.
The electrical pulses generated by the SCS stimulation system, or other neural system, are also referred to as “stimulation pulses”. In an SCS system, the stimulation pulses typically have the effect of producing a tingling sensation, also known as a paresthesia. The amplitude of the stimulation pulses affects the intensity of the paresthesia felt by the patient. In general, it is desirable to have the amplitude of stimulation comfortably set to a level which produces paresthesia to block pain but not above a level that may actually result in pain apart from the native pain. Moreover, the stimulus amplitude should be set to a stimulus level lower than that which can recruit reflex motor nerves that can cause involuntary muscle contractions.
SCS and other stimulation systems are known in the art. For example, an implantable electronic stimulator is disclosed in U.S. Pat. No. 3,646,940 that provides timed, sequenced electrical impulses to a plurality of electrodes. As another example, U.S. Pat. No. 3,724,467 teaches an electrode implant for neuro-stimulation of the spinal cord.
In addition to pain caused by injury to the nerve in the spinal area, chronic pain may also be caused by neuropathic conditions. Such neuropathic conditions include those caused by anginal pain and those caused by peripheral vascular diseases. Neuropathic pain can often be successfully relieved by applying electrical stimulation to the affected area of the body, either via peripheral nerve or spinal cord stimulation.
Chronic pain patients often have reduced exercise capacity as well as limited physical movement. In many cases, it is the chronic pain condition which prevents the patient from having an active life or from pursuing any forms of exercise. One goal of therapy for those suffering from chronic pain is to encourage patients to increase their physical activity. However, up to now, with exception of verbal feedback recounting a patient's own activity, there has been no reliable method to monitor patient activity or inactivity.
Accordingly, what is needed is a system for measuring cardiac rhythm parameters in patients as an adjunct to SCS and other stimulation treatments for chronic pain.